Molecular characteristics of permanganate- and dichromate-oxidation-resistant soil organic matter from a black-C-rich colluvial soil

Abstract

Samples from a colluvial soil rich in pyrogenic material (black C, BC) in north-west Spain were subjected to K2Cr2O7 and KMnO4 oxidation and the residual soil organic matter (SOM) was NaOH-extracted and analysed using analytical pyrolysis–gas chromatography–mass spectroscopy (Py-GC/MS) and solid-state 13C cross-polarisation magic angle spinning–nuclear magnetic resonance (13C CP MAS-NMR) in order to study the susceptibility of different SOM fractions (fresh, degraded/microbial, BC and aliphatic) towards these oxidising agents. Untreated samples that were NaOH-extracted were also analysed. The Py-GC/MS and 13C NMR indicated that KMnO4 promotes the oxidation of carbohydrate products, mostly from degraded/microbial SOM and lignocellulose, causing a relative enrichment of aliphatic and aromatic structures. Residual SOM after K2Cr2O7 oxidation contained BC, N-containing BC and aliphatic structures. This was corroborated by a relatively intense resonance of aromatic C and some signal of alkyl C in 13C NMR spectra. These results confirm that dichromate oxidation residues contain a non-pyrogenic fraction mainly consisting of aliphatic structures.

Molecular properties of ultrafiltered dissolved organic matter and dissolved black carbon in headwater streams as determined by pyrolysis-GC⿿MS

“…This is in agreement with the significant correlation between benzonitriles and PAHs for this sample set (r 2 =0.67; P<0.05). Finally, the detection of indole and diketodipyrrole pyrolysis products are indicative of relatively intact proteinaceous precursors in DOM [43], not of chitin or DBC.…”

Molecular characterization of charcoal to identify adsorbed SOM and assess the effectiveness of common SOM-removing pretreatments prior to radiocarbon dating

“…The presence of the FAs might therefore be an indication for the adsorption of SOM. However, Suárez-Abelenda et al (2014) found significant enrichment of C 16 and C 18 fatty acids after oxidation of SOM with K 2 Cr 2 O 7. These fatty acids are the most abundant fatty acids in all the charcoal samples studied in this study, so this might not only be an artefact of the ABOx treatment but an artefact of the pyrolysis.…”

The chemical composition of native organic matter influences the response of bacterial community to input of biochar and fresh plant material

“…The EG soil treatments (including both control and OA-amended samples) were associated with higher abundances of i) short/mid-chain aliphatic moieties (mostly n-alkanes ranging between C 17 and C 24 ,likely produced by microbial chain length shortening of longer chain aliphatic structures; Buurman et al 2007); ii) mono-and polycyclic aromatic compounds (accumulated upon decay due to their intrinsic recalcitrance; Buurman et al 2005); iii) polysaccharide-derived compounds including methylbenzofuran (Ps11), dibenzofuran (Ps16), and to a lower extent furfuraldehyde (Ps6) and cyclopentenone (Ps8) (all proposed as indicators of degraded SOM formed by bacterial and fungal activities; Buurman et al 2007;Suárez-Abelenda et al 2014; and iv) N-compounds including pyridine (N2), C 1 -pyrrole (N3), phenylpyridine (N10), the chitin marker diketopiperazine compound (N12), and diketodipyrrole (N11). Pyridines, pyrroles and indoles may originate from microbial activities Schulten et al 1997;Suárez-Abelenda et al 2014). Acetamides and diketopiperazine are pyrolysis products of chitin and chitin-entangled protein, respectively (Stankiewicz et al 1997).…”

“…The relative abundances of the pyrolysis products were expressed as the proportion (%) of total quantified peak area (TQPA; the sum of all identified peak areas). These were grouped based on their possible sources Suárez-Abelenda et al 2014) as follows: (i) n-alkanes (C 9:0 -C 33:0 ); (ii) n-alkenes (C 9:1 -C 30:1 );; (iii) n-methyl ketones (C 13:0 -C 35:0 ; K); (iv) n-fatty acids (C 5:0 -C 24:0 ; FA) and (v) other alkenes (Al); (vi) phenol and alkyl phenols (Ph); (vii) ligninderived methoxyphenols (Lg); (viii) benzene-containing compounds (including Ar+B 3 -B 28 ), (ix) polycyclic (PA + NA) aromatic hydrocarbons; (x) N-containing products, (xi) polysaccharide fragments (Ps), and (xii) sterol derived compounds (St). Due to the multiple possible origins of N-compounds, this group was split into three sub-groups: i) pyridines + pyrroles (associated to microbial-derived fractions when present along with tracers of degraded SOM); ii) chitin-derived N compounds (N5+N12, fungi-and arthropods-derived), and (iii) alkyl amides (AM) and indoles (N8, N9) − likely plant-derived, and nitriles (N6, N7) from charred material Suárez-Abelenda et al 2014).…”